Coal against biomass, measured at the lungs rather than the ledger

Most plants compare fuels by calorific value per ton. This one compares them by what turns up in workers' lungs and in the water around the site — the cost that never appears on a quotation.

What leaves the stack when coal burns

PM2.5 — particulate fine enough to pass through the alveoli into the bloodstream, linked to respiratory and cardiac disease.

Sulphur dioxide. Coal carries significant sulphur; burning it produces SO2, the cause of acid rain and acid corrosion in the stack.

Nitrogen oxides, formed at high combustion temperature, which react in the atmosphere to form secondary particulate.

Heavy metals — mercury, arsenic and cadmium carried in the coal, accumulating in soil and water through ash and leachate.

How biomass differs

Far less sulphur. Wood carries a fraction of coal's sulphur, so SO2 falls substantially and acid corrosion in the stack with it.

No heavy metals from the fuel itself. The mercury and arsenic in coal come from strata laid down over millions of years. A tree grown across 20–25 years carries none of it.

Carbon on a short cycle. A tree absorbs CO2 while growing and releases it when burned — a cycle of ten to twenty years, against coal releasing carbon locked underground since long before it.

The part that has to be said plainly

Biomass is not pollution free. Combustion still emits particulate and NOx, and burned incompletely it emits more than it should.

Wood ash is high in potassium, which lowers the ash fusion temperature and means furnace temperature has to be controlled to avoid slagging. That is a technical problem to manage, not an advantage.

The genuine advantages are lower sulphur and no fuel-borne heavy metals, plus the short carbon cycle. Not zero emissions. Anyone telling you biomass is clean is selling something.

The part usually left out: field burning

In Southern Thailand, rubberwood stumps and roots from replanting are commonly burned in the open — no air control, no dust collection, many fields at once in the dry season.

Bringing that material into a controlled furnace therefore cuts particulate by more than a fuel-for-fuel comparison suggests, because it displaces the worst burning at the source.

Read on: rubberwood stumps and roots

If you are weighing a change

Start by co-firing at a low ratio and collect real data. See the method on the replacing coal with biomass page, or call +66 92 392 2292.